The present invention relates to processing circuitry for video endoscope systems and in particular to video processing circuitry for electronically correcting the image orientation of a folded optical imaging system wherein the optical image is reversed.
Video endoscope systems are now well-known in the art of endoscopy. Various endoscope systems are described in U.S. Pat. No. 4,253,447 to Moore and U.S. Pat. No. 4,074,306 to Kakinuma. Such systems include light units which generate alternating fields of colored light for production of color images at the display, although the principles of endoscopy are equally, though less usefully, applied in black and white imaging as well.
The insertion tube of the endoscope provides access and visibility into body cavities. Typically the insertion tube contains a fiber optic light guide for directing light into the cavity to be viewed, an optical focusing section for gathering and focusing the reflected light, an image sensor for providing electrical output in response to the light input, electrical circuitry and connection means for triggering the image sensor and for transmitting signals back to a control unit.
Light transmitted through the fiber optic light guide is reflected from the cavity into which the viewing head is inserted. The optical imaging system gathers and focuses the reflected light to form an image on a solid state image sensor in the viewing head. The image sensor transmits an electrical signal back to the control unit in response to the intensity of light reflected within the cavity. The signal is processed according to its control unit and then later merged into a composite video signal compatible with a monitor.
In addition to the components which are associated purely with image production, it is also desirable, and practically speaking necessary, to include a biopsy channel, and water and air delivery channels.
Because these features must all be contained within the insertion tube of the endoscope, and because the overall diameter of the insertion tube is limited by the human anatomy, it is of paramount importance to optimize space utilization in the insertion tube.
In conventional video endoscope systems, the imaging system at the distal end of the insertion tube conventionally places a solid state rectangular image sensor in a perpendicular orientation with respect to the optical axis of the imaging system and to the central axis of the insertion tube. Because the image sensor in such endoscopes is oriented perpendicular to the optical axis, the size of the image sensor is limited. In addition, since the image sensor provides a rectangular surface area greater than the circular surface area of the optical focusing section, it is difficult to package the biopsy channel, light guide and other features required to be contained within the insertion tube.
Because it is desirable to minimize the size of the distal end of the endoscope while at the same time obtaining maximum used the area of view of the optical system and sensor, a compact optical imaging system has been devised, as described in copending patent application Ser. No. 06/611,618, for a Compact Optical Imaging System, with specific application to video endoscopy, which maximizes the space utilization in the insertion tube.
Unlike conventional viewing heads in use in color video endoscopes, the image sensor in the compact imaging system is oriented with its plane other than perpendicular to the axis of the optical focusing section, preferable parallel to the optical axis. To allow this orientation, which is more desirable from the performance stand point, the invention includes means for turning the light away from the optical axis so that the light rays impinge on the image sensor even though the image sensor is oriented away from the objective lens optical axis. In the preferred embodiment, the image from the focusing section is turned 90 degrees to the image sensor by a glass wedge having a surface for internal reflection.
By placement of the image sensor in a plane parallel to the optical axis, an image sensor having a diagonal measurement which is substantially larger than the diameter of the optical focusing section can be utilized. By this devise, the compact optical imaging system thus provides a viewing head in the insertion tube of an endoscope which optimizes space utilization and permits the use of a substantially larger image sensor and the support of associated electrical circuitry.
The viewing head thus configured however suffers from the drawback, heretofore not adequately overcome, that the image produced at the sensor is reversed with respect to the image orientation which would be correct according to the specifications of the sensor manufacturer, due to the presence of the mirror in the optical path between the object lens and the sensor.
Accordingly, a need exists for an apparatus to correct the image reversal for display on a conventional video monitor such that the image thereby displayed is properly oriented.